The present invention relates to an image forming apparatus detachably provided with a cartridge in which process materials such as an image carrier are integrally assembled.
In order to obtain color images by means of an electrophotographic method, an apparatus is provided in which a color image is formed in such a manner that: a latent image is formed based on the number of separated colors of a document image. Development by color toner is repeatedly conducted so that color toner images can be superimposed on a photoreceptor drum or a photoreceptor belt; and the formed color toner images are transferred onto a transfer sheet so as to obtain a color toner image. The basic process of the aforementioned multicolor color image formation is disclosed in the Japanese Patent Publication Open to Public Inspection Nos. 75850/1985, 76766/1985, 95456/1985, 95458/1985, and 158475/1985, which are applied by the inventors.
In the multi-color image forming apparatus by which a color image can be obtained by the aforementioned superimposing process, a plurality of developing units, in which different color toners are contained, are provided around a photoreceptor, and generally the photoreceptor is rotated a plurality of times so that latent images can be developed into a color image.
In the aforementioned image forming apparatus, the following structure is adopted. That is, some of the image forming means are provided in a cartridge. For example, replace the photoreceptor and the cleaning member, the lives of which are limited, can be replaced, by use of a cartridge. The cartridge can also supply developer carrier and developer toner when they are consumed. In the case of an image forming apparatus of a digital system, a laser writing system is utilized for the latent image forming means to form an image on the surface of a photoreceptor. In the case of the aforementioned laser writing system, some units are integrally formed into a cartridge so as to be detachably provided to the apparatus body.
In the aforementioned image forming apparatus, the process cartridge can be easily maintained, and further, when the process cartridge is removed from the apparatus body, the image transfer region can be widely opened, so that jam clearance of a transfer sheet, inspection of the conveyance surface and cleaning can be conducted with ease. Various, proposals have been made in which a conveyance passage for a transfer sheet, onto which an image is formed by an image forming means, is opened in order to take out a jammed transfer sheet easily.
However, it is troublesome to open the passage of a transfer paper by hand after the cartridge has been removed from the apparatus. Further, if the cartridge is inserted into the apparatus by mistake when the conveyance passage is opened, there is a possibility of the units becoming damaged.
Further, a transfer electrode charged with high voltage, a fixing roller heated at high temperature and members to convey transfer papers are disposed in the transfer region. When they are exposed upon removal of the process cartridge, it is dangerous to touch them carelessly, so that it is necessary to provide a safeguard.